Hepatic acyl CoA profiles obtained from liver biopsy samples with Reye syndrome and control subjects suggested a model of hepatic fatty acid oxidation in which the peroxisomes might play a prominent role. This project will assess the end products of peroxisomal B-oxidation and determine the effect of mitochondrial inhibitors on peroxisomal fatty acid oxidation in isolated rat liver peroxisomes. Rates of fatty acid oxidation in rat liver hepatocytes will be measured in cells obtained from control animals and rats treated with peroxisomal proliferating drugs in the presence and absence of inhibitors specific for mitochondria and hopefully peroxisomes, permeabilized cells will be used initially to afford greater control of substrate and inhibitor supply to the peroxisomes and mitochondria. These studies are intended to probe the interplay between mitochondria and peroxisomes and to determine the source of the different end products of fatty acid oxidation. Fibroblasts from patients with Reye syndrome have been shown in preliminary studies to have altered intracellular Ca responses to extracellular agonists including loss of purinergic and vasoactive agonist responses and enhanced sensitivity to tumor necrosis factor. In addition the Ca2+ responses of both control and patient fibroblasts to several agonists was markedly altered by growth in fatty acids. Studies will be undertaken to fully characterize the agonist profile of control and patient cells, to determine the effect on agonist profiles of exposure of cells to high free fatty acids and to probe the mechanism by which fatty acids affect signal transduction. If a genetically altered receptor response is documented, studies will be instituted to determine the effects of the agonist whose signal transduction is affected on fatty acid oxidation and acyl CoA ester accumulation in rat liver to compare with data already obtained in liver samples from patients. Together, these studies should aid in understanding the mechanism of inhibition of fatty acid oxidation in Reye syndrome, determine whether patients with Reye syndrome have a genetic defect in receptor-mediated signal transduction and assess the relationship btween such a receptor defect and fatty acid oxidation. At a more basic level, these studies should increase our knowledge of the role of peroxisomes in fatty acid oxidation and provide new insight on the effect of high free fatty acids on signal transduction.